The Twin Arrows Navajo Casino Resort
is a destination resort in a rural location about 25 miles east of Flagstaff, Ariz. As a flagship property of the Navajo Nation Gaming Enterprise (NNGE), the 267,000-sq-ft gambling and hospitality venue includes more than 1,000 slot machines, a conference center, indoor pool, restaurants, and a 200-room hotel. To protect the facility from utility power outages caused by the area’s frequent thunderstorms and high winds, NNGE selected an advanced 4-MW standby power system from Cummins Power Generation
“Reliable backup power is critical for us as a gaming facility,” said Jim Wanamaker, facilities manager for NNGE
. “For us, life safety is always of the utmost importance. Beyond that, the critical requirement for us as a gaming operation is that we don’t lose power to the gaming floor or the gaming slot systems to maintain play on the floor. Security systems are also crucial: if security were to go down, we’d have to shut down the gaming systems as well.”
The resort was designed by the Friedmutter Group architects of Las Vegas in collaboration with the Navajo tribal members and JBA Consulting Engineers. To ensure power is available at all times, Twin Arrows
has several redundant systems that include dual utility feeds, multiple uninterruptible power supply (UPS) systems, and a pair of standby diesel generators in a 2N configuration.
The two standby generators operate at 480 V and produce 2 MW each. With a current total facility load of about 1.25 MW, one generator is sufficient to supply the total load in the event of an outage. The second or redundant generator provides several advantages: it is a backup to the first generator, it allows maintenance to be performed without jeopardizing system reliability, and, in an extended outage, it can take over if the first generator consumes its 24-hour supply of fuel.
The generators also operate in parallel and share load using the Cummins PowerCommand digital generator controls and parallel with the utility grid using the PowerCommand digital master control (DMC 300). When an outage occurs, both generators start and assume load. However, the digital master control will shut down the redundant generator when the facility load drops below 80% of a single unit, saving fuel and engine wear. Each generator is housed in a sound-attenuated enclosure, located outdoors.
The casino’s first line of defense is the facility’s three UPS backup units. The battery-powered units maintain power to key casino operations that include emergency lighting, security and surveillance, gaming floor and player management systems, HVAC, and other systems. The UPS systems bridge the approximate 10-second gap between when normal power goes out and the load is assumed by the diesel generators.
Soft-loading, closed-transition design eliminates disruptions
“The standby power system is set up as a prioritized system so that the emergency systems, such as the fire pump, fire alarm, and smoke control systems get the highest priority,” said Leslie Fernandez, senior electrical engineer with Las Vegas-based JBA Consulting Engineers. “The second priority is the legally required standby systems, such as emergency lighting and elevators, followed by business-critical equipment that includes security systems and the gaming floor. The soft-loading, closed-transition design allows the generator sets to assume the load or transfer the load back to the utility in a smooth, controlled way so that voltage and frequency transients (sags) are avoided.
The configuration of the Cummins DMC 300 paralleling system was selected after another manufacturer’s system was ruled out as too costly. “With the simpler Cummins design, it became easier to isolate one or two sections of the common bus without the danger of an adjacent bus becoming energized,” said Chris Tornillo, power systems manager with Cummins Rocky Mountain. “This will allow work to be performed on the de-energized bus with the appropriate minimum personal protection equipment.”
Final validation testing with facility loads and a load bank on the generators were completed in early 2013 in preparation for the resort’s May 2013 grand opening. The facility has experienced several utility outages since the standby system was installed and, according to Wanamaker, the system’s performance has been exceptional. This means Twin Arrow guests can enjoy the casino and hotel facilities no matter what the weather—and save their luck for the games.
All major active systems for the Twin Arrows resort were designed using building information modeling (BIM), Fernandez said. Architects created an extremely detailed 3-D computer model of the structure, with engineers from JBA Consulting Engineers and others, such as the lighting designers, adding their systems. Ultimately, the coordinated efficiencies of BIM helped to reduce costs on the project. View a fly-through video tour of the resort’s BIM design
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